Where is the throat ?

[tmc-okc]

OK, I am going to show my ignorance but I have researched everything I know and haven't found the answer. We are going to limit this discussion to revolvers only and cast boolits. Everything I read says that when purchasing a boolit mould or sizing die the barrel and cylinder throat should be slugged to determine the max size desired for the cast boolit. I understand the barrel may be pinched at the frame junction and therefore may be smaller than the balance of the barrel. And I understand that we cant do much about that. But I don't understand what is being referred to as the "throat". Is this the forward portion of the cylinder. Is this the forcing cone of the barrel ? On most of my revolver cylinders a forward portion of each cylinder is larger in the inside diameter than the portion of the cylinder that supports / houses the brass cartridge case. Is this the "throat"??
Just trying to understand so I can do it right.

Ron H

[Motor]

OK, I am going to show my ignorance but I have researched everything I know and haven't found the answer. We are going to limit this discussion to revolvers only and cast boolits. Everything I read says that when purchasing a boolit mould or sizing die the barrel and cylinder throat should be slugged to determine the max size desired for the cast boolit. I understand the barrel may be pinched at the frame junction and therefore may be smaller than the balance of the barrel. And I understand that we cant do much about that. But I don't understand what is being referred to as the "throat". Is this the forward portion of the cylinder. Is this the forcing cone of the barrel ? On most of my revolver cylinders a forward portion of each cylinder is larger in the inside diameter than the portion of the cylinder that supports / houses the brass cartridge case. Is this the "throat"??
Just trying to understand so I can do it right.

Ron H

Ron. Don't you mean the forward portion of the cylinder is "smaller" than where the case is supported?

[Bullwolf]

I'll borrow a few pics from Gunblast to demonstrate what is considered the "throat" of a revolver cylinder.


The first picture shows a J-word boolit at the end of the cylinder throat.

http://www.gunblast.com/images/Ruger-NewVaquero/MVC-2019F.jpg


The second pic shows a cylinder throat being measured with pin gauges.

http://www.gunblast.com/images/Brownells_Reamer/MVC-004F-big.JPG

The last picture shows a cylinder throat being reamed with a cylinder reamer.
http://www.gunblast.com/images/Brownells_Reamer/MVC-005F-big.JPG


Hope that helps you understand things a little better.



- Bullwolf

[RED333]

The throat is in the cylinder. If you look in a chamber you will see that there is a step in the place were if loaded the brass ends. The throat is typically about .001-.002 larger in diameter than the bullets fired. It is a more important dimension when firing cast lead bullets.
The begining of a barrel on a revolver is called the forcing cone. It directs the incoming bullet into the rifling.

Bullwolf beat me to it and did a better job.

[Bullwolf]

The forcing cone is after the cylinder, right at the start of the revolver barrel.

The part that is lit up in this image.

http://webpages.charter.net/nemo288/ForcingCone624.jpg



- Bullwolf

[IraqVet1982]

Great pics bullwolf!

[tmc-okc]

Gentlemen, Thank you for your very educational, clear and concise replies. Last night, using the information you provided, I measured the chamber & throat area of 2 pistols. (1) S&W 24-2 3 inch 44 Spec. (2) S&W 29-2 6 inch nickel 44 Mag. I also pulled up the cartridge and chamber drawing for the SAAMI website. With your aid and the SAAMI drawings I now more fully understand as to how the cylinders are made and the importance of proper case length and sizing the boolit to the size of the throat. And I even understand WHERE the throat of the cylinder is now - LOL

Thank you - Motor, Bullwolf & Red333 for your precise information and the practical pictures provided.
While I am a long time reloader ( 35 + years ) I am new to the casting game. I have yet to cast my first boolit but just about have all materials and equip. in place to begin smelting. Next thing I believe I need to do is slug the barrels and throats of both these pistols to determine what the final size of the cast boolits should be.

Ron H

[detox]

In revolvers the cast bullet is sized .001-.002 over cylinder's free bore (throat) diameter. This reduces leading by preventing gas cutting past bullet..

In rifles the cast bullet is sized for a slip fit (under .0001-.0005) to free bore or leade diameter. This improves accuracy by centering bullet better in leade just before forcing cone or throat.


Here is a diagram of rifle chamber.

[WALLNUTT]

I like my revolver bullets right at or .0005 under throat diam. A slight resistance through the throat with a sized bullet.

[captaint]

Well, OKC, you're approaching this from the right direction. You're doing research before - not after. This will help you along the way. And, as Detox said - in a perfect world, half a thou (boolit diameter) under throat dimension will be just the ticket. If you can, do remove the cylinder for slugging. In some guns, this is really easy. Others, not so much. Mike

[dakotashooter2]

Also keep in mind that you want the throat to be slightly larger than the bore. You don't want to be sizing down the bullet as it passed through the throat and making it too small for the bore. That is why throats are sometimes reamed

[Motor]

Ron, Not saying you are over thinking this because way too many under think things. A lot depends on your exspectations too.

Nearly all of my cast pistol loads, are fired at no more than 50 yards. I use Lee molds and shoot everything "as cast" no boolit sizing. My ammo is accurate, maybe not match accurate but still good and I have no leading problems after load development that also includes alloy hardness.

Personally, I think sometimes its eaiser to fix problems with shooting cast than trying to prevent them. I think of it as trying to fix something that is not malfunctioning. Its much eaiser to fix when its not working.

Motor

[tmc-okc]

Gentlemen, I have all sorts of lead products ready for smelting. I have wheel weights (segregated between stick on & clip on), I have some lead sheets, some really thick lead sheets (cant bend them with my fingers), 50/50 solder, old fishing sinkers and other odds & ends. I plan on smelting & marking them separately into ingots so I can identify each type later - no mixing at this point. After smelting I intend to pour pure soft lead slugs in the approx. correct diameter to allow me to slug the bore, forcing cone and throats of each of my revolvers - all 6 of them. From that point I can cast a few boolits in each of the moulds I have obtained from which I can determine the "as cast" diameter and determine what should be done from there. Really not trying to "Over Think" things just trying to get started in casting right. I know that if my cast boolits don't shoot worth beans during the early stages of this hobby I am very likely to have one of two things happen. I'll spend even more time cleaning lead out of the barrels or I'll give up entirely. So for my best long term situation I want to get it as right as possible right out of the gate. I already have a problem with my good old SAECO Mod 24 furnace in that it is a leaker. I need to empty the pot and scrub it completely clean and see if I can get the seat to close completely.

Thanks for all the excellent information and encouragement.

Ron H

[runfiverun]

you can lap the stem to the spout to make it stop.

when you start getting into cast boolit shooting, you really are getting into learning your guns better.
I have learned just about enough to change my sig-line again...